Re: [PATCH 3/3] cxl/region: Fix state transitions after reset failure

[Dan Williams <dan.j.williams@intel.com>]

Jonathan Cameron wrote:
> On Fri, 16 Jun 2023 18:24:39 -0700
> Dan Williams <dan.j.williams@intel.com> wrote:
> 
> > Jonathan reports that failed attempts to reset a region (teardown its
> > HDM decoder configuration) mistakenly advance the state of the region
> > to "not committed". Revert to the previous state of the region on reset
> > failure so that the reset can be re-attempted.
> > 
> > Reported-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> > Closes: http://lore.kernel.org/r/20230316171441.0000205b@Huawei.com
> > Fixes: 176baefb2eb5 ("cxl/hdm: Commit decoder state to hardware")
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> LGTM - though maybe even nicer if we can be pretty sure this will succeed
> before trying it.. (same comment as previous patch)

I had the same reaction, but satisfied myself that this is something
that userspace can manage. I.e. tooling can effectively predict when the
kernel will complain about this ordering situation and prevent it. In
other words, the only way this happens in practice is if userspace makes
a mistake.

It is already the case that partially committed decoders need to be
tolerated by the platform since setup and teardown are not atomic. So I
think 'cxl destroy-region' is where this follow-on smarts belongs.

> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks for the collaboration as always.